Near atmospheric carbon dioxide activates plant ubiquitin cross-linking

Background Identifying CO 2 -binding proteins is vital for our knowledge of CO 2 -regulated molecular processes. The carbamate post -translational modification is a reversible CO 2 -mediated adduct that can form on neutral Nterminal alpha-amino or lysine e -amino groups. Methods We have developed triethyloxonium ion (TEO) as a chemical proteomics tool to trap the carbamate post -translational modification on protein covalently. We use 13 C-NMR and TEO and identify ubiquitin as a plant CO 2 -binding protein. Results We observe the carbamate post -translational modification on the Arabidopsis thaliana ubiquitin e -amino groups of lysines 6, 33, and 48. We show that biologically relevant near atmospheric PCO 2 levels increase ubiquitin conjugation dependent on lysine 6. We further demonstrate that CO 2 increases the ubiquitin E2 ligase ( At UBC5) charging step via the transthioesterification reaction in which Ub is transferred from the E1 ligase active site to the E2 active site. Conclusions and general significance Therefore, plant ubiquitin is a CO 2 -binding protein, and the carbamate post -translational modification represents a potential mechanism through which plant cells can respond to fluctuating PCO 2 .